The present invention relates in general to optical couplers and in particular to a new and useful optical coupling device which is capable of coupling a light transmitter and light receiver to a single optical waveguide.
Such a coupling element is usable particularly in optical waveguide communication systems with duplex or multiplex operation. Systems of this kind have the advantage that for a simultaneous duplex operation at longer distances, such as of some kilometers, a single light (optical) waveguide is needed.
FIG. 1 shows such a system for two transmitting and/or receiving stations T1 and T2 which are optically coupled to each other by a waveguide LWL. Each transmitting and/or receiving station comprises a transmitter S1, S2, such as a semiconductor laser, with the two transmitters sending out radiations of unequal wavelengths .lambda.1, .lambda.2, a receiver E1, E2 such as a photodiode, and a wavelength-dependent coupling element, a duplexer D1, D2, by which the transmitter and the receiver of a transmitting and/or receiving station are coupled to the waveguide. Such a coupling element produces the effect that the radiation mixture transmitted in the lightwave guide LWL in opposite directions passes to the desired receiver, and that no undesired radiation passes to the transmitters. For example, the radiation sent out by transmitter S1 and having a wavelength .lambda.1 arrives only at receiver E2 (and not at the receiver E1). This path is indicated by arrows.
Such an arrangement is disadvantageous and not economical since the transmitter, receiver, and duplexer in a transmitting and/or receiving station are individual component parts which are coupled to each other by optical means, for example optical waveguides. Such a coupling requires time consuming and expensive adjustment and assemblage. Also, considerable optical losses are to be taken into account since there are many locations of optical coupling, for example splices between the component parts and the optical paths.